|Publication number||US5587934 A|
|Application number||US 08/630,195|
|Publication date||Dec 24, 1996|
|Filing date||Apr 10, 1996|
|Priority date||Oct 21, 1993|
|Publication number||08630195, 630195, US 5587934 A, US 5587934A, US-A-5587934, US5587934 A, US5587934A|
|Inventors||William W. Oldfield, Thomas R. Brinkoetter, Todd D. Antes|
|Original Assignee||Wiltron Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (13), Non-Patent Citations (5), Referenced by (35), Classifications (4), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This is a continuation of application Ser. No. 08/140,781 filed Oct. 21, 1993, abandoned.
1. Field of the Invention
The present invention relates to the calibration of vector network analyzers in general and in particular to an automatic calibration apparatus therefor which does not require the use of "perfect" calibration standards.
2. Description of the Related Art
Microwave and RF vector network analyzers (VNA) require calibration to enhance the accuracy of the system. Typically the calibration consists of measuring known "perfect" standards and transferring the accuracy of the standards to the VNA.
In practice, prior known calibration techniques typically require the connection of at least three standards between the test ports of a VNA as well as the pressing of a multiplicity of front panel buttons in a correct sequence. This is a time consuming process requiring a certain level of expertise. Verifying the accuracy of the calibration is also a time consuming process requiring expertise.
In view of the foregoing, principal objects of the present invention are a method and apparatus comprising an automatic VNA calibration apparatus which requires an operator to simply connect a calibration/verification box to each one of two test ports on a VNA and press one button. The apparatus then automatically calibrates the VNA and verifies the calibration.
Externally the calibration/verification box comprises a pair of RF connectors for connecting the box to the VNA test ports and connectors for coupling the box to a controller.
Internally the box comprises one set of microwave/radio frequency (RF) components for calibrating the VNA, another set of RF components for verifying the accuracy of the VNA after it has been calibrated and two multi-throw switches for placing the RF components between the VNA test ports during the calibration and verification operations.
The RF components do not have to be perfect and even if they were, their perfection would be masked by the switches. However the RF connectors connecting the calibration/verification box to the VNA test ports are carefully measured in each of the available switch positions.
The controller, which may be incorporated in the VNA, is provided with a calibrate button/switch to initiate the calibration and verification operations and is programmed to control the sequence of the operation of the two multi-throw switches, to process the measured S-parameters of the RF components at the VNA test ports in each of the switch positions in a conventional manner, to use the information obtained to correct any inaccuracies in the VNA, and to verify the corrections made. Optionally, the controller may also be provided with a second button/switch for initiating a separate or additional verification operation any time after the initial calibration/verification.
As indicated above, a principal advantage of the apparatus and method of the present invention is that the RF components used for calibrating the VNA do not have to be "perfect" so long as their S-parameters are accurately measured and stored for use by the controller. If they are accurately measured and stored, the information can be used for calibration. Of course, the measured artifacts should have the same general characteristics as those of a test standard. For example, one of the RF components could provide a low loss, low reflective through-connection between the test ports. Another could terminate each of the test ports with a low reflection characteristic line (e.g. matching) impedance. Another RF component could short the terminals to ground so as to provide a highly reflective termination producing a phase shift of 180 degrees.
Still another RF component/switch position could "open" the terminals, i.e. provide an infinite impedance, so as to provide a highly reflective termination providing a phase shift of zero (0) degrees.
In general, while four or more RF components could be used for calibration, only three components are necessary so long as the S-parameters of the three components are known and widely separated over the Smith chart.
For purposes of verification, two additional RF components are provided for providing, respectively, a through-line and an attenuation for producing known signal S-parameters.
The elimination of the requirement for "perfect" standards allows the various calibration and verification artifacts to be incorporated into a single connection "box". The system controller performs all of the necessary adjustments required of the calibration sequence, relieving the operator of the task. The controller then evokes the verification sequence after the calibration is complete.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description with reference to a drawing in which FIG. 1 shows a block diagram/schematic of a calibration/verification box and controller coupled to a VNA according to the present invention.
Referring to FIG 1, there is provided in accordance with the present invention an automatic vector network analyzer (VNA) calibration apparatus designated generally as 1. In the apparatus 1 there is provided a calibration/verification box or housing 2 for housing a plurality of electrical components and a programmable controller 3. The housing 2 and controller 3 are coupled to a VNA 4.
In the housing 2 there is provided a first and a second terminal 10 and 11. Each of the terminals 10 and are provided with microwave/radio frequency (RF) connectors for connecting the housing 2 to corresponding RF connectors on corresponding test ports/terminals 12 and 13 on the VNA 4.
In the interior of the housing 2 there is provided a multi-throw switch assembly designated generally as 20 having a plurality of at least five positions 1-5 for coupling predetermined electrical components between the first and second terminals 10, 11. For example, the switch assembly 20 has a first position for coupling a through-line between the terminals 10 and 11 so as to allow the transmission of a signal from the first terminal 12 to the second terminal 13 on the VNA 4 with a known magnitude and phase shift; a second position for selectively coupling a substantially non-reflective termination to each of said first and said second terminals 12, 13 located on said VNA 4, respectively; and a third position for selectively coupling each of said first and said second terminals 12, 13 located on said VNA 4 to a termination which causes the signal incident thereon to be reflected with a known magnitude and phase shift, respectively. Each of the switch positions 1-3 are used during calibration of the VNA.
In general, while more than three RF components could be used for calibration, only three are necessary so long as their respective S-parameters are known and widely spaced in terms of a Smith chart.
For purposes of verifying the accuracy of the VNA 4 after it has been calibrated, the switch assembly 20 is provided with at least two additional switch positions, i.e. positions 4 and 5, for selectively coupling at least a first and a second verifying electrical component between the first and second terminals 10, 11 on the housing 2. For example, the first electrical component used for verification comprises an electrical component which is constructed so as to allow the transmission of a signal from said first terminal 12 on said VNA 4 to said second terminal 13 on said VNA 4 with known S-parameters as a function of frequency. The second electrical component used for verification comprises an attenuator having a known attenuation and phase shift as a function of frequency. In a preferred embodiment of the present invention, the first verifying electrical component, which may be located at the position 5 of the switch 20, comprises a Beatty standard.
In operation, the operator merely connects the terminals 10, 11 of housing 2 to the terminals 12, 13 of the VNA 4 by means of the RF connectors and presses a calibration button 14 on the controller 3. The system controller 3, which is suitably programmed in any well known manner, then performs the necessary tasks required for calibration and verification. These tasks include switching the multi-throw switch 20 to couple the above-described discrete electrical components to the terminals of the VNA in a predetermined sequence, measuring the S-parameters at the VNA ports for each switch position, comparing this information with stored information as to the expected values for each of the switch positions and using all of the information thus obtained to correct the inaccuracies of the VNA. Thereafter, the controller moves the switch 20 to positions 4 and 5 to verify the accuracy of the calibrations.
To provide for verification of the calibrations at a subsequent time there is further provided a verify button 15 on the controller 3 for re-verifying the calibration at any time that the verification button is depressed.
The particular sequence in which the calibration and the verification of the VNA 4 occurs is not important so long as the selected sequence is noted and the proper processing of the VNA signals corresponds to the selected sequence.
While a preferred embodiment of the present invention is described above, it is contemplated that numerous modifications may be made thereto for particular applications without departing from the spirit and scope of the present invention. For example, if measurements of S-parameters of a device occur at frequencies other than a frequency at which the VNA is calibrated, well known interpolation functions may be used to interpolate and store the error terms between calibration points. Accordingly, it is intended that the embodiments described be considered only as illustrative of the present invention and that the scope thereof should not be limited thereto but be determined by reference to the claims hereinafter provided.
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|Jun 10, 1997||CC||Certificate of correction|
|Jul 6, 1999||AS||Assignment|
Owner name: ANRITSU COMPANY, CALIFORNIA
Free format text: CHANGE OF NAME;ASSIGNOR:WILTRON COMPANY;REEL/FRAME:010052/0559
Effective date: 19971001
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